a(n) = 12^n - n.

Terms

a(0) =1a(1) =11a(2) =142a(3) =1725a(4) =20732a(5) =248827a(6) =2985978a(7) =35831801a(8) =429981688a(9) =5159780343a(10) =61917364214a(11) =743008370677